Great question, Cindy! I usually try to avoid study guides as a general rule. But not all study guides are created equal. Some are full of twaddly busy work and others have very useful information and supplemental ideas.
For example, my sister-in-law loved the study guide that came with one of the Opal Wheeler composer biographies (can’t remember which one right now). It had information on the geography and some cultural recipes, among other things. However, some other “study guides” from a different place turned out to be nothing but a bunch of worksheets when I flipped through them.
I guess I like them if they are more of a teacher resource of supplemental/additional/enrichment ideas to select from, not a list of direct questions for the student.
Just my $.02 worth. 🙂